iio: core: Add iio_read_acpi_mount_matrix() helper function

The ACPI "ROTM" rotation matrix parsing code atm is already duplicated
between bmc150-accel-core.c and kxcjk-1013.c and a third user of this
is coming.

Add an iio_read_acpi_mount_matrix() helper function for this.
The 2 existing copies of the code are identical, except that
the kxcjk-1013.c has slightly better error logging.

To new helper is a 1:1 copy of the kxcjk-1013.c version, the only change
is the addition of a "char *acpi_method" parameter since some bmc150
dual-accel setups (360° hinges with 1 accel in kbd/base + 1 in display)
declare both accels in a single ACPI device with 2 different method names
for the 2 matrices. This new acpi_method parameter is not "const char *"
because the pathname parameter to acpi_evaluate_object() is not const.

The 2 existing copies of this function will be removed in further patches
in this series.

Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20240425125754.76010-2-hdegoede@redhat.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/Makefile

@@ -7,6 +7,7 @@ obj-$(CONFIG_IIO) += industrialio.o
 industrialio-y := industrialio-core.o industrialio-event.o inkern.o
 industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
 industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
+industrialio-$(CONFIG_ACPI) += industrialio-acpi.o
 
 obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
 obj-$(CONFIG_IIO_GTS_HELPER) += industrialio-gts-helper.o

drivers/iio/industrialio-acpi.c

@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* IIO ACPI helper functions */
+
+#include <linux/acpi.h>
+#include <linux/dev_printk.h>
+#include <linux/iio/iio.h>
+#include <linux/sprintf.h>
+
+/**
+ * iio_read_acpi_mount_matrix() - Read accelerometer mount matrix info from ACPI
+ * @dev:		Device structure
+ * @orientation:	iio_mount_matrix struct to fill
+ * @acpi_method:	ACPI method name to read the matrix from, usually "ROTM"
+ *
+ * Try to read the mount-matrix by calling the specified method on the device's
+ * ACPI firmware-node. If the device has no ACPI firmware-node; or the method
+ * does not exist then this will fail silently. This expects the method to
+ * return data in the ACPI "ROTM" format defined by Microsoft:
+ * https://learn.microsoft.com/en-us/windows-hardware/drivers/sensors/sensors-acpi-entries
+ * This is a Microsoft extension and not part of the official ACPI spec.
+ * The method name is configurable because some dual-accel setups define 2 mount
+ * matrices in a single ACPI device using separate "ROMK" and "ROMS" methods.
+ *
+ * Returns: true if the matrix was successfully, false otherwise.
+ */
+bool iio_read_acpi_mount_matrix(struct device *dev,
+				struct iio_mount_matrix *orientation,
+				char *acpi_method)
+{
+	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+	char *str;
+	union acpi_object *obj, *elements;
+	acpi_status status;
+	int i, j, val[3];
+	bool ret = false;
+
+	if (!adev || !acpi_has_method(adev->handle, acpi_method))
+		return false;
+
+	status = acpi_evaluate_object(adev->handle, acpi_method, NULL, &buffer);
+	if (ACPI_FAILURE(status)) {
+		dev_err(dev, "Failed to get ACPI mount matrix: %d\n", status);
+		return false;
+	}
+
+	obj = buffer.pointer;
+	if (obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 3) {
+		dev_err(dev, "Unknown ACPI mount matrix package format\n");
+		goto out_free_buffer;
+	}
+
+	elements = obj->package.elements;
+	for (i = 0; i < 3; i++) {
+		if (elements[i].type != ACPI_TYPE_STRING) {
+			dev_err(dev, "Unknown ACPI mount matrix element format\n");
+			goto out_free_buffer;
+		}
+
+		str = elements[i].string.pointer;
+		if (sscanf(str, "%d %d %d", &val[0], &val[1], &val[2]) != 3) {
+			dev_err(dev, "Incorrect ACPI mount matrix string format\n");
+			goto out_free_buffer;
+		}
+
+		for (j = 0; j < 3; j++) {
+			switch (val[j]) {
+			case -1: str = "-1"; break;
+			case 0:  str = "0";  break;
+			case 1:  str = "1";  break;
+			default:
+				dev_err(dev, "Invalid value in ACPI mount matrix: %d\n", val[j]);
+				goto out_free_buffer;
+			}
+			orientation->rotation[i * 3 + j] = str;
+		}
+	}
+
+	ret = true;
+
+out_free_buffer:
+	kfree(buffer.pointer);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_read_acpi_mount_matrix);

include/linux/iio/iio.h

@@ -788,6 +788,19 @@ static inline struct dentry *iio_get_debugfs_dentry(struct iio_dev *indio_dev)
 }
 #endif
 
+#ifdef CONFIG_ACPI
+bool iio_read_acpi_mount_matrix(struct device *dev,
+				struct iio_mount_matrix *orientation,
+				char *acpi_method);
+#else
+static inline bool iio_read_acpi_mount_matrix(struct device *dev,
+					      struct iio_mount_matrix *orientation,
+					      char *acpi_method)
+{
+	return false;
+}
+#endif
+
 ssize_t iio_format_value(char *buf, unsigned int type, int size, int *vals);
 
 int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer,